It is well known to those skilled in the art that honeycomb core turbine seals fabricated from stainless steel are widely utilized in jet engines and it is also known that one of the major problems encountered in the installation of honeycomb seals in jet engines is the location and securement of said seals within and to the conventional mounting rings which are utilized to install the seals in the jet engine in juxtaposition to the blades of the turbine.
There have been various means and methods proposed and utilized by the prior art to accomplish the desired installation of honeycomb seals in mounting rings. Among them are the use of a welding procedure which is commonly known as "spike welding." This entails the installation of the seal in the mounting ring and the resistance welding of the seal to the adjacent surface of the mounting ring by use of a resistance welding electrode. The problem arising from the utilization of the spike welding method is that it frequently results in damage to seals because of the insertion of the welding electrode into the cells of the honeycomb core.
Due to the damage to the rub surface of the seal resulting from the spike welding method, it is necessary to machine said rub surface to remove dents and burns caused by said method. Obviously, the necessity for such machining subsequently to the spike welding of the core seal to the associated mounting ring entails expensive and time-consuming handling of the seal/mounting ring combination. The best machining of the rub surface is done by electrical discharge machining.
Other methods of affixing the seals in mounting rings include the provision of a resinous tape which carries a brazing alloy, said tape being located at the interface between the seal and the mounting ring before the mounting ring/seal composite is placed in a high-temperature brazing furnace.
The tape is rolled into the OD of the core under considerable pressure. The major disadvantage of the utilization of such tapes is the necessity for the out-gassing of the resinous component of the tape during the brazing process which materially slows the brazing process and also results in the need to exhaust the gasses resulting from the breakdown of the resin carrier to prevent permanent contamination of the inert atmosphere in the brazing furnace. The out-gassing process consumes a considerable amount of time and, thus, materially adds to the cost of the resulting seal composite.
A common method of applying braze alloy powder to the honeycomb core seal is to mix the alloy powder with a resinous vehicle and apply the mixture to the OD of the core seal. The mixture is then allowed to dry prior to the insertion of the seal into the mounting ring.
Once again, the significant cost factor arising out of this process is the necessity for out-gassing the resinous constituents of the vehicle. Furthermore, before the brazing powder can wet to the core seal and mounting ring (which usually takes place after out-gassing), the powder particles can move and, since the assembly is almost always positioned in the furnace with the seal axis vertical, the powder particles can shift downwardly due to gravity and create a thicker bond joint on the bottom edge of the seal.
For further elucidation of the type of seal utilized in gas turbine engines of the character under discussion here, reference is made to U.S. Pat. No. 4,618,152, entitled HONEYCOMB SEAL STRUCTURE, issued Oct. 21, 1986.